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Pharm > ANS Pharmacology - Parasympathetics > Flashcards

ANS Pharmacology - Parasympathetics Flashcards

1
Q

Sites of action of acetylcholine in peripheral nervous system

A

Preganglionic fibers to ANS ganglia

Preganglionic fibers to adrenal medulla

Parasympathetic postganglionic fibers

Sympathetic postganglionic fibers innervating sweat glands (anomaly!)

NMJ

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2
Q

Muscarine

A

Parasympthomimetic

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3
Q

Nicotine

A

Acts as stimulant —> desensitizes sympathetic/parasympathetic

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4
Q

Acetylcholine

A

Both sympathetic / parasympathetic

Nicotinic vs muscarinic action

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5
Q

Acetylcholine biosynthesis

A

Addition of acetyl CoA to choline > ChAT choline acetyltransferase (cytoplasmic enzyme)

Pre-formed ACh transported into vesicles, no intracellular metabolizing enzymes

Choline from diet/protein metabolism (from serine)

RLS = Transport of choline into nerve terminal

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6
Q

Drugs affecting ACh synthesis / release

A

Hemicholinium : blocks choline uptake

Vesamicol : blocks transport into vesicles

Cholineacetyltransferase : none to date

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7
Q

Botulinus toxin

A

Bind to cell membrane + internalized > Block fusion of vesicles with plasma membrane (cleaves synaptobrevin) > block transmission

From Clostridium botulinum

Flaccid paralysis of muscles; death by paralysis of respiratory muscles

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8
Q

Mechanism of synaptic transmitter release

A

Nerve depolarization > voltage gated Na/Ca channels > Ca depended vesicle fusion and exocytosis > diffusion into synaptic cleft > receptor binding and activation > transmitter breakdown

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9
Q

Termination of acetylcholine action

A

Enzymatic breakdown of ACh by acetylcholinesterase

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10
Q

Acetylcholinesterase

A

Terminates ACh action at nerve terminals

Attached on pre/post-synaptic membrane by collagen-like filaments

Very rapid action, 150 microsec turnover

Cleaves bond to form Acetate/choline - choline re-uptake (RLS)

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11
Q

Pseudocholinesterase

A

Synthesized in liver, found in plasma

Function unclear

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12
Q

Nicotinic sites in PNS

A

Preganglionic fibers to all ANS ganglia

Preganglionic fibers to adrenal medulla

NMJ

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13
Q

Muscarinic sites in PNS

A

Parasympathetic post-ganglionic fibers

Sympathetic postganglionic fibers innervating sweat glands

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14
Q

Nicotinic receptors

A

Nicotinic neuronal - Nn
Nicotinic muscle - Nm

Ligand-gated ion channels “ionotropic receptors”

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15
Q

Muscarinic receptors

A

GPCR

“Metabotropic receptors”

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16
Q

Activation of Nicotinic ACh receptors

A

ANS ganglion stimulation - both sympathetic and parasympathetic

Release of EPI/NE from adrenal gland

Contractions of skeletal muscle

CNS - tremor, anxiety, sleep disturbances, resp/circ center effects

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17
Q

Nicotinic receptor structure/ activation

A

Pentameric structure; a, b, y, d subunits

Two a subunits —> each bind ACh to open channel —> Na moves in, K moves out

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18
Q

Muscarinic receptor structure/activation

A

7TM GPCR receptor

  • gland secretion (sweat, salivary, mucous, lacrimal)
  • contract smooth muscle (airway, GI, gall bladder, urinary, ureters)
  • pupillary constriction
  • relax sphincters (GI, urinary, biliary)
  • show HR

SLUMD (salivation, lacrimation, urination, defecation, miosis)

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19
Q

M2 - muscarinic type II receptor

A

Heart, smooth muscle, autonomic ganglia

Inhibitory

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20
Q

M3 - muscarinic type III receptor

A

Exocrine glands, smooth muscle, blood vessels (endothelium)

Excitatory

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21
Q

Action of M2 receptors

A

Inhibitory in cardiac muscle

Inhibition of adenyl ate cyclase + activation of K+ channels (decreases potential > harder to depolarize)

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22
Q

Action of M3 receptors

A

Excitatory in smooth muscle

Opening of plasma membrane and intracellular Ca channels

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23
Q

Parasympathomimetic drugs

A

Therapeutic uses (agonists): ophthalmology (glaucoma), urinary tract disorders, GI tract disorders

Side effects: Salivation-lacrimation-urination-defecation-miosis; abdominal pain; severe hypotension

24
Q

Examples of parasympathomimetic drugs

A

Acetylcholine (no significant therapeutic applications, broad spectrum, poorly absorbed orally/subq, rapidly hydrolzyed by IV admin)

MEthacholine
Carbachol
Bethanecol

25
Q

Methacholine

A

Synthetic analog of acetylcholine
Reduced susceptibility to hydrolysis, more selective for Muscarinic

Used for diagnosis of asthma

CV side effects - limited clinical use

26
Q

Carbachol

A

Carbamylated ACh
Resistant to AChE

Both muscarinic + nicotinic activity
Limited clinical use due to ganglionic stimulation

Used to induce miosis, treatment of glaucoma

27
Q

Bethanecol

A

Methylated + carbamylated ACh
Resistant to AChE

Very selective for muscarinic over nicotinic

Used to test pancreatic function, treat urinary retention (stimulate bladder contraction)

28
Q

Naturally occuring Cholinergic alkaloids

A

Pilocarpine - S Am shrub pilocarpus; mainly muscarinic, 100x potency of ACh; pronounced action on salivary/sweat glands; opthalmologocial use; can inc BP/tachycardia

Arecoline - from “betel nut”, no therapeutic uses, previously de-wormer

Muscarine - from mushroom; high dose —> death; atropine = antidote

29
Q

Atropine

A

Anti muscarinic agent
Naturally occuring - in Belladona

M»»»N receptor antagonist

Tachycardia, dec intestinal contraction/motility, drying airway/sinuses/bronchodilation; pupillary dilation, tremor, CNS delusion/excitment

30
Q

Therapeutic uses of atropine

A

Preanesthetic - decrease respiratory secretions
OTC cold medications - dec lacrimal/nasal secretions
Anti-asthmatic medication

Ophthalmology - mydriasis

Cough suppression in vet med with hydrocodone

31
Q

Homoatropine

A

Anti muscarinic

More rapid onset that atropine
Shorter duration of action
Less potent

32
Q

Scopolamine

A

Antimuscarinic

Pre-anesthesia to decrease resp secretions
OTC motion sickness

Same peripheral action as atropine, but pronounced sedative action

Sedate mentally ill patients

33
Q

Propantheline

A

Synthetic antimuscarinic

No BBB penetration - no CNS unless high dose

Mitigate GI spasm/secretions (spasmodic colic in horses)
Reduce rectal tearing risk in rectal exam
Reduce spasm/promote relaxation of esophagus during choke in horses

34
Q

Tropicamide

A

Short duration of action

Used in ophthalmology > mydriasis

Short recovery time (preferred over atropine)

35
Q

Iris/lens innervation

A

Parasympathetic —> miosis (contract); muscarinic agonist same effect

Sympathetic —> mydriasis (dilate); muscarinic antagonists same effect

36
Q

Mydriasis

A

Radial (dilator) muscle - contraction causes pupil dilation, innervated by sympathetic

Muscarinic antagonists

37
Q

Miosis

A

Circular (sphincter) muscle - constriction of pupil, innervated by parasympathetic

Muscarinic agonist

38
Q

Ciliary muscle

A

Contraction —> lens bulges - near vision accommodated

Relaxation - lens flattens - far vision accommodated

Innervated by parasympathetic system (ACh mediated)

39
Q

Cyclopelgia

A

Paralysis of ciliary muscle - lack ability to accommodate
Can happen with too much or too little ACh

40
Q

Paralysis of Accomodation

A

Muscarinic antagonist —> simulates too little ACh present

Absence of contraction —> lungs flatted; far-sightedness

41
Q

Spasm of accomodation

A

Muscarinic agonists of AChE inhibitors —> simulate too much ACh

Ciliary muscle constant maximal contraction > lens budged; near sightedness

42
Q

Treatment of narrow angle (acute congestive) glaucoma

A

Miosis with pilocarpine and physostigmine > inc drainage

Reduce pressure until surgery

Muscarinic antagonists can precipitate an attack

43
Q

Treatment of wide angle (open angle, chronic, simple) glaucoma

A

Surgery!

Mechanism of drug action unclear
Use pilocarpine/physostigmine

44
Q

B-blockers in the eye

A

Decrease production of aqueous humor

45
Q

Synthetic nicotinic agents

A

Directly or indirectly modify Nicotinic Cholinergic receptor activity

Ganglionic stimulants
Ganglionic blockers
AChE inhibitors

46
Q

Ganglionic stimulants

A

Nicotine - complex often unpredictable physiological responses, stimulation + desensitization; CNS effects; stimulates adrenal medulla to release NE/EPI, Nicotinic receptor in skeletal muscle (no significant therapeutic uses)

47
Q

Ganglionic blockers

A

Hexamethonium - blocks ganglionic nicotinic receptors (Nn) not Nm; limited use - both sympathetic/parasympathetic

Trimethaphan - has been used in vet med to lower BP during surgery

48
Q

AChE inhibitors

A

Inhibit breakdown of ACh —> parasympathomimetic

Side effects: muscarinic actions at autonomic effector organs, nicotinic action at ANS ganglia, nicotinic stim at NMJ (followed by desensitization > flaccid paralysis), CNS effects

49
Q

Classes of AChE inhibitors

A

Reversible inhibitors - reversible
Carbamylating inhibitors - prolonged
Phosphorylation inhibitors - irreversible

50
Q

Reversible AChE inhibitor

A

Edrophonium

Competitive inhibitor, no covalent attachment

Rapidly reversible, short acting

Used to diagnosis Myasthenia gravis (weakness of contraction due to decrease in receptor density at NMJ)

51
Q

Carbamylated inhibitors of AChE

A

Breakdown produces carbamate vs acetate —> much slower to release

52
Q

Physostigmine

A

Plant derived alkaloid
AChE inhibitor

Absorbed well from GI, crosses BBB

Originally used in myasthenia gravis to inc ACh at NMJ
Used in glaucoma
Used in atropine poisoning

53
Q

Other carbamylating AChE inhibitors

A

Neostigmine (only peripheral effects - used currently to treat myasthenia gravis, no BBB cross)

Pyridostigmine (shorter half life)

Demecarium

54
Q

Phosphorylation inhibitors of AChE

A

Organophosphate

Diisopropyl fluorophosphoric acid

used in insecticide products
synthesis of new AChE required to recover

Nerve gases, Sarin, VX gas

55
Q

Toxicology of O-P poisoning

A
  1. Overstimulation of muscarinic / nicotinic ACh receptors (SLUMD)
  2. Overstimulation of ACh receptors at NMJ in skeletal muscle
  3. Paralysis of diaphragm / thoracic muscles > resp failure
  4. CNS effect
56
Q

O-P poisoning antidote

A

Pralidoxime (2-PAM)
Phosphate acceptor

Only effective before “aging” process (1-3 h)

57
Q

Therapeutic uses of anticholinesterases

A

Glaucoma
During Anethesia
Myasthenia gravis
Atropine poisoning

Pharm (10 decks)

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